AUSMELT®/ISASMELT™ non-ferrous smelters drop moist solid feeds from above into a tall cylindrical furnace with a matte/metal/slag bath while also blowing oxygen-enriched air down in through a submerged vertical lance. (AUSMELT® of Outotec, and ISASMELT™ of Glencore Technology.) Once fully melted, the matte/slag is periodically tapped into another furnace for separation. These are often referred to as Top Submerged Lance (TSL) furnaces.
The AUSMELT top submerged lance technology optimizes feed material dissolution, energy transfer, reaction, primary combustion, and other critical processes which all take place in the slag layer inside the smelter vessel. Submerging the gas injection ensures that reactions occur rapidly and residence times will be low due to an intense agitation that is caused in the vessel. The degree of oxidation and reduction can be controlled by adjusting the fuel:oxygen ratio supplied to the lance, and the proportion of reductant coal to feed. This easy way to control the oxidation and reduction enables the furnace to be selectively operated between strongly oxidizing through strongly reducing conditions. Operating temperatures in AUSMELT top submerged lance furnaces can range from 900° C. to 1400° C.
ISASMELT furnaces are top-entry submerged-lance upright-cylindrical shaped steel vessels that are lined with refractory bricks. Inside at the bottom of the furnace, in the “liquid zone”, is a molten bath of slag, matte, or metal. A hollow steel lance is lowered into the bath through a hole in the roof of the furnace, and air or oxygen-enriched air is forcefully injected through the lance to agitate the bath.
Mineral concentrates and other materials are dropped into the bath from above through a hole in the roof. If suitably fine, such materials can also be injected down the lance with the air. An intense reaction results in a small volume when the feed materials contact, heat, and react with the oxygen in the injected gas.
Lances may include “swirlers” that force the injected gas to vortex against the walls inside to more effectively cool the lance's walls. Outside of the lance, a layer of slag will freeze on the air-cooled walls. Such frozen slag helps isolate the steel lance from the surrounding temperatures which could be high enough to melt the lance if contacted directly. But ultimately the steel tip of all submerged lances will wear out from the immediately surrounding violence and need replacement. The good news is worn lances are easily refurbished and replaced. The worn tips are simply cut off and new tips are welded onto the original lance body.
ISASMELT furnaces typically operate in the range of 1000-1200° C., depending on their application. The refractory bricks that line the inside floors and walls of the furnaces are there to protect the steel shell from the severe heat inside the furnace that would otherwise quickly melt the steel shell.
Refractory bricks are subject to corrosion, wear, uneven heating, swelling with ingrained melt, and fractures because they are brittle. But the refractory bricks in the liquid bath zone of a furnace are especially subject to corrosion and thinning. So as they corrode and thin, they are less able to support the weight of refractory brick wall lining above. (Conventional practice has been to direct the entire weight of the complete refractory brick wall lining vertically down to its ring footing.) Embodiments of the present invention divide the weight amongst one or more upper tiers each fitted with cantilevered shelves.
Smelted products are removed from furnaces through tap holes in a procedure called “tapping”. Such tapping can be continuous, or done in batches. At the end of a tap, the tap holes can be closed by blocking them with clay plugs. They can be reopened by thermic lances and/or by drilling. Alternatively, the melt can be removed from the furnace using either an underflow or an overflow weir for continuous discharge of molten material.
The smelted products thus tapped will separate on their own once they arrive and settle in a rotary holding furnace, an electric furnace, a settling vessel, a melt-transporting ladle, or granulated.
Most of the large amount of energy needed for smelting that is used to heat and melt sulfide concentrates and feed materials is a product of the reaction of oxygen with sulfur and iron in the concentrates. A small amount of supplemental energy that is needed to balance out losses is supplied by injecting coal, coke, petroleum coke, oil, or natural gas to react with the injected air. Solid fuels are best added through the top of the furnace along with the feed materials, and liquid and gas fuels can be injected with the air forced down inside the lance.
Eventually all furnaces reach the ends of their campaign lives. Such ends-of-life are preferably planned for and expected, rather than catastrophic, as can occur with a refractory-brick wall collapse.
The furnaces we are concerned with here stack refractory-brick in walls that are not fixed to the inner walls of the steel vessels. The bricks in these walls wear differently due to variances in abrasion, corrosion, and other factors that occur below the bath level and above the bath level.
Conventional furnaces of this type stacked all the refractory-brick in the walls in one uninterrupted pile. Some include floating cooling blocks in these stacks that moved with the brick under thermal expansion forces. Each row of brick and floating cooling blocks has to support the weight of every row above it and pass that weight down until the burden reaches the furnace floor.
The portion of refractory-brick walls at the bottom around the bath zone has to bear the most weight and is subject to severe wear.